Bad service

I am very much annoyed at this point, my account is paid up with MTN however I am still harassed by their debt collectors demanding money. I called MTN they advised my account is closed and paid up however I requested for a paid up letter on the 14 October 2022 and 30 days later on the 11 of November 2022 I received a response that my payment hasn’t been allocated and yet I made the payment on the 10th of October 2022. Debt collectors keep increasing the money they say I owe, who on earth m I owing at this point!!! Would never take up anything or encourage anyone to take any contract with MTN!!